feat(web): worktree toggle + cleaner new-session wizard

[X-Skoprio]

Description

The web dashboard's "New session" wizard always created a git worktree on a new branch — there was no way to say "just run the agent in the repo folder." The TUI exposes this; the backend already supports it (worktree_branch: Option<String> in CreateSessionBody, gated at src/session/builder.rs:228); only the web UI was forcing a value.

This PR closes that gap and tightens the wizard flow:

• New "Create a worktree" toggle on the wizard. Off ⇒ frontend sends worktree_branch: undefined and create_new_branch: false, and the backend takes the existing no-worktree path. Default stays on, so existing behaviour is unchanged.
• Restructured wizard from 3 steps (Project → Settings → Review) into 4 linear steps (Project → Session → Agent → Review). Title and the worktree toggle/branch name now live on a dedicated Session step rather than being buried under "Advanced settings" on the Settings step.

No backend or API changes — CreateSessionBody.worktree_branch was already Option<String> and create_new_branch was already a bool.

Files changed

• web/src/components/session-wizard/SessionWizard.tsx — adds useWorktree to WizardData; submit body branches on it; new step ordering.
• web/src/components/session-wizard/StepIndicator.tsx — adds "session" to StepId.
• web/src/components/session-wizard/steps/SessionStep.tsx — new component (title + worktree toggle + branch/worktree name).
• web/src/components/session-wizard/steps/AgentStep.tsx — removes the title/branch inputs (moved to SessionStep), keeps agent / sandbox / yolo / advanced.
• web/src/components/session-wizard/steps/ReviewStep.tsx — Branch row label is now "Branch / worktree" (since the branch name is also the worktree dir name); shows "None — runs in repo folder" when worktree is off.

PR Type

• New Feature

Checklist

• I understand the code I am submitting
• New and existing tests pass
• Documentation was updated where necessary
• For UI changes: included screenshot or recording

(Docs unchanged — this is a UI-only refinement of an existing feature, not a new public API. Happy to add a screenshot in a follow-up commit if maintainers want one inline.)

How I tested

• cargo fmt --check clean
• cargo clippy --features serve --all-targets -- -D warnings clean
• cargo test --features serve — 1700+ passing, 0 failed
• cd web && bun run build clean (TypeScript + Vite)
• Manually exercised both modes in aoe serve --no-auth: worktree-on creates a new worktree (git worktree list grows); worktree-off runs in the repo folder (git worktree list and git branch --show-current unchanged).

AI Usage

• AI was used for drafting/refactoring

AI Model/Tool used: Claude Code (Opus 4.7)

Any Additional AI Details you'd like to share:
Used Claude Code to explore the codebase, draft the wizard restructuring, and draft this PR description. All design decisions and the final review were done by me.

• I am an AI Agent filling out this form (check box if true)

[Seluj78]

Very good idea thanks!

Even though it's only in beta, I feel like it's very important to have the web UI match the TUI as much as possible! I can't test it right now but looking at the PR on my phone it looks good.

[njbrake]

Hi @X-Skoprio thanks so much! Would you mind attaching a screenshot or screen recording of the functionality?

[X-Skoprio]

@njbrake Sure, here are some screens :